Uncontrolled activation of macrophages promotes various inflammatory diseases. The most devastating diseases linked to macrophage activation include atherosclerosis, a global health burden. To discover novel regulators of macrophage activation as therapeutic targets, we performed global proteomics on IFN?- triggered M1 and IL-4-induced M2 macrophages. We identified PARP9 and PARP14, ADP-ribosylation enzymes, as key candidates. The functions of these two PARPs have not yet well characterized and their roles in macrophage biology or vascular disease are unknown. Based on our own preliminary findings, this multidisciplinary research project will test the novel hypothesis that PARP9 promotes and PARP14 suppresses macrophage activation. In Specific Aims 1 and 2, we will use mouse models to examine the role of PARP9 and PARP14 in macrophage activation and atherosclerosis. Our pilot studies have demonstrated many new findings on the interplay between PARP9 and PARP14 and their associations with pro-inflammatory STAT1 and anti-inflammatory STAT6. Specific Aim 2 also will use mass spectrometry and systems biology to explore the mechanisms by which the interactions between PARP9 and PARP14 regulate macrophage activation via ribosylation of signaling molecules (e.g., STAT1). Our study will reveal novel mechanisms of macrophage activation and provide a proof of concept that PARP9 and PARP14 can be therapeutic targets for atherosclerosis and its complications. Furthermore, the study will offer new insight into the shared mechanisms for various other inflammatory diseases, leading to exciting future directions and clinical translation.